AS, in antiquity, a particular weight, consisting of 12 ounces; being the same with libra, or the Roman pound. The word is derived from the Greek as, which in the Doric dialect is used for us, one, q. d. an entire thing; though others will have it named as quasi as, because made of brass.
As was also the name of a Roman coin, which was of different weights and different matter in different ages of the commonwealth. Under Numa Pompilius, according to Eusebius, the Roman money was either of wood, leather, or shells. In the time of Tullus Hostilius, it was of brass; and called as libra, libella, or pondo, because actually weighing a pound or 12 ounces. Four hundred and twenty years after, the first Punic war having exhausted the treasury, they reduced the as to two ounces. In the second Punic war, Hannibal pressing very hard upon them, they reduced the as to half its weight, viz. to one ounce. And, lastly, by the Papirian law, they took away half an ounce more, and consequently reduced the as to the diminutive weight of half an ounce: and it is generally thought that it continued the same during the commonwealth, and even to the reign of Vespasian. The as, therefore, was of four different weights in the commonwealth. Its original stamp was that of a sheep, ox, or sow: but from the time of the emperors, it had on one side a Janus with two faces, and on the reverse the rostrum or prow of a ship.
As was also used to denote any integer or whole. Whence the English word ace. Thus as signified the whole inheritance; whence heres ex asse, the heir to the whole estate.